Modeling Multipath Dispersion

The focus of the previous two chapters was design; chapter 2 examined optics design, and chapter 3 examined electronics design. In contrast, this chapter investigates the properties of the wireless infrared channel itself, over which the designer has no control. Specifically, we examine the severity of multipath dispersion in typical indoor environments, and assess its effect on system performance. We present a recursive method for calculating the impulse response of a room with Lambertian reflectors [57][58]. The method, which accounts for multiple reflections of any order, enables accurate analysis of the effects of multipath dispersion on high-speed indoor optical communication. We present a simple algorithm for computer implementation of the technique. We present computer simulation results for both line-of-sight and diffuse transmitter configurations.Inboth cases we find that reflections of multiple order are a significant source of intersymbol interference. We also describe experimental measurements of optical multipath, which help verify the accuracy of our simulations.